This invention relates to a liquid chemical grouting apparatus for grouting liquid chemicals into the ground to improve the same and a valve switching arrangement in a conduit system for supplying liquid chemicals to the apparatus.
In the past, as this type of liquid chemical grouting apparatus, an apparatus has been known which is devised by one of the inventors of the present invention and disclosed in Japanese Patent Publication No. 60-3576.
In the prior art apparatus, an outer pipe has, at its tip end, a boring cutter and an inner pipe is disposed in the outer pipe so as to be spaced from the outer pipe. The inner pipe has, near its tip end, an annular wall which blocks the space and which are formed with first and second holes at predetermined circumferential intervals. Formed in the outer pipe is a discharge hole which is normally in communication with the first hole. A piston valve urged to be normally raised by means of a spring is received in the inner pipe near its tip end. When the piston valve is raised, the first hole is closed by the piston valve and concurrently the second hole is opened to permit the space to communicate with an opening at the tip end of the outer pipe. When the piston valve is lowered, the first hole is opened to communicate with the interior of the inner pipe and at the same time the second hole is opened to permit the space to communicate with the interior of the inner pipe.
With the piston valve raised, when a fluid component is supplied to the space between the inner and outer pipes, the fluid component flows into the opening at the tip end of the outer pipe through the second hole and when fluid components are respectively supplied to the space between the inner and outer pipes and to the inner pipe, one fluid component supplied to the inner pipe acts to lower the piston valve by its liquid pressure, permitting the other fluid component supplied to the space between the inner and outer pipes to flow into the inner pipe through the second hole and mix with the one fluid component, and a mixed fluid component is injected to the outside through the first hole and discharge hole.
Conversely, with the piston valve lowered, when the supply of the fluid component to the inner pipe is stopped, the piston valve is permitted to return to its raised position under the influence of only upward force of the spring. During this operation, a hydrostatic pressure prevailing in the inner pipe and sliding resistance exert on the piston valve and therefore the spring is disadvantageously required to have a large spring force which can overcome the above exerting force. Further, in order to lower the piston valve in opposition to the large spring force, the fluid component must be supplied at a large pressure, raising a problem that the supplied fluid component tends to leak, and a countermeasure for prevention of leakage has to be taken.